Inflammation, the brain and energy metabolism – it’s like the trifecta in chronic fatigue syndrome (ME/CFS) research. It seems like virtually everyone in the ME/CFS field believes that all three are involved but that belief only carries so much weight in a small field. What this field really needs is buy-in from outside researchers who can help move it forward.

That appears to have happened recently when a major research group lead by Robert Dantzer penned a review paper proposing that low-grade inflammation is causing energy production problems in chronic fatigue syndrome (ME/CFS) and probably many other diseases. The authors didn’t shy away from the chronic fatigue syndrome (ME/CFS) connection. In fact, they lead their review paper off with it, placing the fatigue in ME/CFS in the same context as the fatigue in cancer, MS, rheumatoid arthritis and others.

The study was published in the Frontiers in Neuroscience journal series which is touted as the 1st most cited series in the Neurosciences journal field.

The Dantzer group’s involvement in the intersection between inflammation and energy production is welcome but not entirely surprising; it’s a logical outcome of their past work. Dantzer spearheaded the now accepted idea that the immune system produces the symptoms of “sickness behavior” (fatigue, headache, muscle aches, sore throat, etc.) that occur during an infection which serve to reduce our energy usage and to keep us isolated from others (they posit to prevent pathogen spread).

What’s new is his group’s focus on the energy production process itself – a focus, interestingly, made possible largely by the work of ME/CFS researchers. The piece, with lead author Tamara LaCourt, shows how low-grade inflammation can cause the same energy problems we’re seeing in ME/CFS: a metabolic switch from energy-efficient, oxygen-based energy production process to a fast-acting, inefficient glycolysis-based approach.

Immune cells aren’t like other cells; jumping into action causes them to rev their motors up tremendously, placing enormous stress on their energy production systems. As they do this, they switch from a focus on aerobic energy metabolism to what the authors call “aerobic glycolysis” in order to churn out energy more quickly. That process results in less mitochondrial energy production and the increased production of toxic by-products like lactate. Plus, over time this process results in reduced nutrient availability and less energy for the rest of the body.

The authors believe that inflammation and metabolic and energy problems come together to produce a final common endpoint: fatigue.

Several studies from the Solve ME/CFS Initiative are examining whether the energy production of immune cells in ME/CFS is up to the task.

Prolonged inflammation also tends to result in two other energy production problems: increased insulin resistance and reduced glucose tolerance. Reduced glucose tolerance smacks glucose uptake by immune cells at the very time that they’re clamoring for it, causing the body to break down fats and proteins, thus removing resources it would ordinarily use elsewhere. In yet another whack at the energy production, inflammation increases reactive oxygen species production which can hammer mitochondrial energy production.

The authors believe that neurons – which rely on glycolytic processes in astrocytes to get their energy – may be hit hardest by chronic inflammation. This is because insulin resistance – a common outcome of chronic inflammation – destroys the glycolytic process in astrocytes, causing neurons to get their energy from fats – a slower and less efficient process.

Miller’s work on ME/CFS suggests that problems with the basal ganglia – the dopamine-producing center of the brain – may be causing problems with movement, reward and fatigue in ME/CFS. That’s a particularly interesting finding given that dopaminergic neurons in the brain are particularly vulnerable to inflammation. Shungu’s studies, which have consistently found high lactate and low gluthathione levels in the ventricles of ME/CFS patients brains, suggest that high levels of oxidative stress could be causing inflammation in the brain itself.

Plus, even low-level inflammation can disrupt a key element in ME/CFS and FM – sleep – which, in turn, increases fatigue. Simply altering one’s circadian rhythm (i.e. one’s sleep times) can have significant metabolic effects, leading to increased glucose levels and decreased insulin sensitivity. The effects don’t end with sleep; sleep deprivation results in the need for increased energy expenditures the next day.

Then add in the extra ten percent in extra energy needs that chronic low-level inflammation imposes on the body – and the potential for a dramatic drop in energy production rises. (We’ll find out more about total energy production in ME/CFS during the metabolic chamber tests in the NIH’s intramural study).

The authors believe that impaired energy production represents a “final common pathway” in persistent fatigue.

Leader in the Field

“In sum, most evidence for an association between fatigue and mitochondrial functioning comes from CFS, indicating lower levels of antioxidants and possible reductions in mitochondrial ATP production.” The authors.

We understandably don’t think of researchers in the small ME/CFS research field as being pioneers in the medical research field at large, but some have ploughed brand new ground. Suzanne Vernon’s computational biology work at the CDC was so novel that an entire issue of the Pharmacogenomics journal was devoted to it. Gordon Broderick and Travis Craddock’s expansion of that work at Dr. Klimas’s Institute of NeuroImmune Medicine has taken computational biology further – much further – in ME/CFS than in any other field. Ron Davis and Mark Davis at Stanford are using new HLA gene typing and T-cell technologies to try and nail down what is activating ME/CFS patients’ immune systems.

ME/CFS researchers’ attempts to understand the intersection between mitochondrial problems and fatigue are clearly breaking new ground as well. According to the authors of this review article, 21 of the 25 studies examining the intersection between mitochondrial problems and fatigue have been produced by ME/CFS researchers. Researchers we all know ( e.g. Naviaux, Montoya, Hornig and Lipkin, Fluge and Mella) were cited again and again in the overview.

The authors even cited Workwell’s groundbreaking 2013 study which indicated that a shift to glycolytic energy production occurred during the second day of a two day exercise test in ME/CFS. They also singled out the 2017 Tomas study which found that under conditions of cellular stress, the mitochondria in ME/CFS patients’ cells were unable to rise to the occasion.

Turning to the metabolomics studies, the authors cited three ME/CFS studies which have pointed to “reduced metabolic activity”. They believe the metabolic changes seen in ME/CFS reflect a chronic over-reliance and eventual depletion and abandonment of lipid metabolism, which results in a greater use of carbohydrate stores; hence the greater reliance on glycolysis and impaired aerobic energy production. In short, the authors believe the metabolomic studies in ME/CFS are demonstrating the same metabolic shift that the authors propose occur in states of chronic low-grade inflammation.

Interestingly, the authors proposed that many ME/CFS patients are probably exceeding their daily energy stores. That, of course, makes perfect sense given Staci Stevens’s and Workwell’s findings that, for some patients, simply sitting upright puts them into an aerobic energy deficit.

For all its possible connections, the idea that fatigue in ME/CFS is simply the result of “low-grade inflammation” seems untenable given the disability present – unless that inflammation is found in the brain. The Simmaron Research Foundation is bringing the brain, the immune system and metabolism together in a way that’s never been seen before in ME/CFS.

The Simmaron Research Foundation’s first ME/CFS cerebral spinal fluid study suggested that an immune dysregulation, the likes of which approached that found in multiple sclerosis, may be present in the ME/CFS patients’ central nervous systems. Their second outlined an atypical ME/CFS subset. Their current CSF (cerebrospinal fluid) study – an expanded version of the first study which includes a metabolomic component – will be the first to potentially merge immune and metabolic findings in the most energetically active part of the body – the brain.

The observed differences in some of the subpopulations of T and NK cells between patients and healthy controls could define a distinct immunological profile that can help in the diagnostic process of ME/CFS patients, contribute to the recognition of the disease and to the search of more specific treatments. Rivas et. Al. 2018

Problems with natural killer (NK) cell functioning have been like an anchor in the storm for immunologists interested in chronic fatigue syndrome (ME/CFS). While other immune results like cytokines have flipped and flopped all over the place, the NK cytotoxic results have been solid. Almost every study has found that when given the chance to kill infected cells, the NK cells in ME/CFS patients poop out. (The studies which have not found differences in NK cell functioning have tended not to use whole blood or used older samples – suggesting that something in the blood could be impairing NK cell functioning in ME/CFS.)

The most extensive study – a year-long 2012 study involving Dr. Peterson and Griffith University in Australia – found reduced natural killer cell functioning at all time points. (Peterson has a long history of interest in natural killer cells; he was a co-author of the first study, over thirty years ago, to find deficient NK cell functioning in chronic fatigue syndrome (ME/CFS).)

NK cells are important because they maintain the lines of our initial immune defense, holding the fort, so to speak, until the big guns – the T and B cells- wipe out the infection. – They also regulate the immune response.

Normally our cells signal that they are infected by displaying peptide fragments from the pathogen (using MHC Class 1 molecules) on their surface. NK cells then hunt out and destroy these infected cells. However, some pathogens have learned how to prevent the cells they’ve infected from displaying these peptide fragments.

If NK cells and other parts of the innate immune response can’t hold back the invaders, the pathogens may invade more deeply into the body, potentially causing more problems before the adaptive immune response (T and B-cells) can kick in.

A deficient early response to pathogens would then very likely translate into more symptoms. We don’t know when the problems with NK cell killing got started in ME/CFS, but if they were in place prior to the illness or occurred early in the illness they could have played a role in the inception of ME/CFS as people who have more trouble fighting off a pathogen; i.e. people with more severe symptoms, are more likely to come down with ME/CFS.

Once ME/CFS has begun, the inhibited NIK killing response could mean more trouble removing tumor and infected cells – particularly herpes virus infected cells- as people deficient in NK cells have trouble fighting off herpes viruses.

NK cells, then, are vitally important, but attempts to identify issues other than cytotoxic killing abilities have been less successful. NK cells come in different types (cytotoxic and regulatory) and the balance of these subpopulations is important. Some studies have found differences in these subpopulations in ME/CFS and some have not.

Many of those studies, however, have been small and used less than stringent criteria for defining ME/CFS. A Spanish group decided to rectify those problems with a more definitive study which examined NK cell populations in a larger study (n=149) with patients who met the Canadian Consensus Criteria for ME/CFS. In order to ensure they captured all factors in the blood that might be whacking NK cells, they used whole blood and analyzed it within 6 hours of collection.

Then they tried to reverse engineer their results to see if a diagnostic test could be developed which simply charted which kinds of NK cells a person had. That was pretty good, but then they went further and asked if people who were worse off had different subpopulations of NK cells or more evidence of herpes virus reactivations (EBV, HMCV).

This larger, fresher (quick analysis of blood), stricter (CCC patients only) and more comprehensive study found differences where others had not – and plenty of them. This group validated – with a high degree of certainty (p = 0.0075) – previous findings of an increased subpopulation of NK cells (NK CD56++(high)) which, get this, excrete more cytokines (particularly IFN-y), possibly causing more symptoms, but which have low cytotoxic activity. Because these cells have unusually long life spans and pump out cytokines that cause more T-cell proliferation, higher numbers of them could contribute to autoimmunity and inflammation.

These cells were particularly high in the group of patients whose illness began without evidence of an infection. The Spanish group suggested that activation of the stress response via the HPA axis and raised levels of catecholamines such as norepinephrine (adrenaline) could have triggered the expansion of this potentially autoimmune affecting natural killer cell subset.

No differences were found, however, in the levels of several receptors (NKp46, NKp30, NKp44) that have been found elevated in some autoimmune/inflammatory conditions (Sjogren’s Syndrome, Crohn’s disease) or reduced in chronic infections (HIV, tuberculosis, influenza, etc.).

Increased levels of the CD 69 marker suggested autoimmunity may be present in ME/CFS

Reduced levels of a receptor (NKG2C) were very common (p<0.0001) in ME/CFS. When this receptor, which is only found in NK cells, is activated by the presence of virally infected cells, it triggers an expansion of NK cells. Not surprisingly, NK cells become dotted with this receptor in people with chronic herpesvirus and other infections (HCMV, EBV) but ME/CFS patients’ NK cells had consistently lower levels of this receptor than did the healthy controls. The authors didn’t speculate why this occurred, but it could involve lower levels of infection in ME/CFS – something Ron Davis is finding in his severely ill cohort – or a problem responding to infections that are present.

That second possibility was buttressed by an inverse correlation found between a marker of infection (CD 57+) and the lower expression of a marker (NKp46) which is often reduced in herpesvirus infections. The authors suggested that the scenario found in ME/CFS (increased cd57+, lower NKp46, high NKG2C) could reflect HCMV (cytomegalovirus) reactivation.

Increased levels of the CD69 marker (p= 0.011) provided another suggestion that ME/CFS may be an autoimmune/inflammatory disease. This important marker, which is found on many immune cells, stimulates NK cell cytotoxic activity. More importantly, CD69 has been described as a master regulator for autoimmunity in rheumatoid arthritis (RA) through its upregulation of TGF-B – one of the very few cytokines that has usually been found increased in ME/CFS.

A “descent” in T regulatory cells similar to that found in autoimmune conditions such as lupus and RA was also found. Finally, an inverted Th17/T regulatory cell ratio, which is also found in autoimmune conditions like lupus, wrapped up the autoimmune connections found in this study.

Using a mathematical classification model, the group was able to correctly diagnose 70% of ME/CFS patients and healthy controls simply by using the findings from this in depth study of natural killer cell populations.

Conclusions

This large Spanish study of NK cell subpopulations found numerous irregularities in NK cell types in ME/CFS, several of which pointed to issues with autoimmunity and/or inflammation. As in other studies, this study indicates that larger is indeed better when it comes to studying ME/CFS.

The study validated prior findings of an unusually large set of NK cells which produce more cytokines – conceivably causing more symptoms and immune activation – but which are less effective at killing infected cells. That finding seemed to jive with a picture of highly symptomatic ME/CFS patients who may have trouble fighting off infections.

While no differences were found in the levels of receptors which can be elevated in autoimmune conditions, several other findings suggested that NK cells may be fighting off herpesvirus infections or may be involved in autoimmune/inflammatory processes in ME/CFS.

Finally, using just NK cell subpopulation data, the authors were able to correctly identify 70% of patients and healthy controls, indicating that significant NK cell differences exist. All told, the study identified several natural killer irregularities that could participate in autoimmunity and dysregulate other parts of the immune system.